JP7699490B2 - Optical system and imaging device - Google Patents

Description

The present invention relates to an optical system and an imaging device.

Optical systems used in video cameras, digital still cameras, and mirrorless interchangeable-lens cameras are required to be small and have high optical performance. One such optical system is known to be made up of three lens groups, a first lens group, a second lens group, and a third lens group, in which the second lens group is movable for focusing, and all three lens groups have positive refractive power (see, for example, Patent Documents 1 to 3).

JP 2019-66585 A JP 2017-167327 A International Publication No. 2019/073744

However, the above-mentioned conventional technologies have room for further study from the viewpoint of achieving both shortening the overall optical length and high optical performance. For example, the technologies described in Patent Documents 1 and 2 are large-diameter optical systems, but the focal length of the first lens group relative to the focal length of the entire system and the focal length of the second lens group relative to the focal length from the object side surface of the first lens group to the lens closest to the image surface of the third lens group are not sufficiently optimized. Therefore, it is insufficient to improve performance while shortening the overall optical length. In addition, the technology described in Patent Document 3 optimizes the focal length of the first lens group relative to the focal length from the object side surface of the first lens group to the lens closest to the image surface of the third lens group, but does not sufficiently optimize the focal length of the second lens group relative to the focal length from the object side surface of the first lens group to the lens closest to the image surface of the third lens group. Therefore, it is insufficient to improve performance while shortening the overall optical length.

The objective of the present invention is to provide an optical system and imaging device that has a short overall optical length and high performance.

In order to solve the above-mentioned problems, an optical system according to one aspect of the present invention is an optical system that comprises, in order from the object side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power, wherein the second lens group is movable along the optical axis so as to change the spacing between adjacent lens groups, wherein the first lens group comprises, in order from the object side, at least a first lens, a second lens, and a third lens, wherein the first lens and the second lens have negative refractive power, and satisfies the following formula:
1.5<f1/f<7.0 (1)
1.5<f2/f<5.0 (2)
however,
f: focal length from the object side surface of the first lens group to the lens closest to the image surface in the third lens group when focusing at infinity; f1: focal length of the first lens group; f2: focal length of the second lens group.

In order to solve the above problem, an imaging device according to one aspect of the present invention includes the above optical system and an imaging element provided on the image plane side of the optical system, which converts the optical image formed by the optical system into an electrical signal.

According to one aspect of the present invention, it is possible to provide an optical system and an imaging device that have a short total optical length and high performance.

FIG. 2 is a diagram illustrating an optical configuration of the optical system of the first embodiment when focused on infinity. 4 is a diagram showing longitudinal aberration of the optical system of Example 1 when focused on an object at infinity. FIG. FIG. 11 is a diagram illustrating an optical configuration of the optical system of Example 2 when focused on infinity. FIG. 11 is a diagram showing longitudinal aberration of the optical system of Example 2 when focused on an object at infinity. FIG. 13 is a diagram illustrating an optical configuration of the optical system of Example 3 when focused on infinity. FIG. 13 is a diagram showing longitudinal aberration of the optical system of Example 3 when focused on an object at infinity. FIG. 13 is a diagram illustrating an optical configuration of the optical system of Example 4 when focused on infinity. FIG. 13 is a diagram showing longitudinal aberration of the optical system of Example 4 when focused on an object at infinity. FIG. 13 is a diagram illustrating an optical configuration of the optical system of Example 5 when focused on infinity. FIG. 13 is a diagram showing longitudinal aberration of the optical system of Example 5 when focused on an object at infinity. 1 is a diagram illustrating an example of a configuration of an imaging device according to an embodiment of the present invention.

[Embodiment 1]
An embodiment of the present invention will be described in detail below. The embodiment of the present invention relates to an optical system suitable as an imaging optical system for a film camera, a video camera, a digital still camera, etc., and an imaging device including the optical system. The optical system and imaging device described below are one aspect of the optical system and imaging device according to the present invention, and the optical system and imaging device according to the present invention are not limited to the following aspects. In this specification, a configuration expressed as "consisting of" means that the configuration is essentially the only one included.

1. Optical System 1-1. Optical Configuration The optical system according to an embodiment of the present invention is composed of, in order from the object side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power. Since each lens group has positive refractive power, it is easy to focus a light beam. Therefore, in this embodiment, it is possible to design a large-diameter optical system.

In this specification, a "lens group" includes one or more lenses, and the spacing between the lenses in the lens group does not change.

In this specification, the lens group may include a cemented lens. When the lens group includes a cemented lens, the number of lenses is the number of lenses that are each cemented together. An example of a cemented lens is a cemented lens in which multiple lenses are integrated together with no air gap between them. In this case, only the multiple lenses that make up the cemented lens are counted. Another example of a cemented lens is a cemented lens in which multiple lenses are integrated together and bonded together by a very thin layer of adhesive that has no substantial optical effect. In this case, the layer of adhesive is not counted as a lens.

The lens group may also include a compound lens in which a single lens and resin are integrated together. For example, a compound lens in which a single lens and resin are integrated together is counted as one lens.

(1) First Lens Group The first lens group is the lens group located closest to the object among the three lens groups constituting the optical system of this embodiment. The first lens group has positive refractive power as a whole. The first lens group has at least a first lens, a second lens, and a third lens in order from the object side, and the first lens and the second lens have negative refractive power. In this way, the lenses from the lens closest to the object side to the second lens in the first lens group are lenses having negative refractive power (negative lenses). In this embodiment, such a configuration makes it possible to achieve a compact size in the radial direction and a wide angle.

Moreover, it is more preferable that the first lens and the second lens are negative meniscus lenses with a convex surface facing the object side. This configuration is preferable from the viewpoints of correcting distortion and coma, achieving a compact size in the radial direction, and realizing a wide angle.

It is also preferable that the first lens group includes at least one cemented lens. This configuration is preferable from the viewpoint of effectively correcting axial chromatic aberration and lateral chromatic aberration that occur throughout the entire optical system. This configuration is also preferable from the viewpoint of reducing the lens spacing and shortening the overall optical length of the optical system.

(2) Second Lens Group The second lens group is a lens group located at the center of the three lens groups constituting the optical system of this embodiment. The second lens group has positive refractive power as a whole. The second lens group is movable along the optical axis so as to change the interval between adjacent lens groups, and in the optical system of this embodiment, it becomes a focus group as described later.

The second lens group is preferably composed of three or fewer lenses. This configuration is preferable from the viewpoint of miniaturizing a driving device such as an actuator for moving the second lens group, thereby miniaturizing the entire lens barrel in the optical system of this embodiment.

In addition, in the second lens group, it is preferable that the lens closest to the object side in the second lens group has a concave surface facing the object side. This configuration is preferable from the viewpoint of effectively correcting image plane fluctuations that occur during focusing.

(3) Third Lens Group The third lens group is the lens group located closest to the image plane among the three lens groups constituting the optical system of this embodiment. The third lens group has positive refractive power as a whole.

It is preferable that the third lens group is composed of three or less lenses. This configuration is preferable from the viewpoint of reducing the number of lenses and shortening the overall optical length. Moreover, it is preferable that the three or less lenses include at least one negative lens, but do not include an aspherical lens. This configuration is preferable from the viewpoint of excellent correction of chromatic aberration and image surface quality.

(4) Other configurations The optical system according to the embodiment of the present invention is composed of only three lens groups, namely, in order from the object side, the first lens group, the second lens group, and the third lens group. No other lens groups are included between the first lens group and the second lens group, between the second lens group and the third lens group, or on the image side of the third lens group. The optical system according to the embodiment of the present invention may further include optical elements other than the above lens groups as long as the effects of this embodiment can be obtained.

It is preferable that the optical system has an aperture. However, the aperture here refers to an aperture that determines the light beam diameter of the optical system, i.e., an aperture that determines the F-number of the optical system. The aperture is preferably disposed between the first lens group and the second lens group. This configuration is preferable from the viewpoint of reducing the effective diameter of the lenses on the object side and image surface side of the aperture. This configuration is also preferable from the viewpoint of reducing the effective diameter of both the object side of the lens having positive refractive power (positive lens) on the object side of the aperture, and the image surface side of the positive lens on the image surface side of the aperture, relatively to the aperture. This configuration is preferable from the viewpoint of suppressing the effect of aberration correction by adjacent lenses.

1-2. Operation during focusing In an embodiment of the present invention, the second lens group is movable along the optical axis so as to change the interval between adjacent lens groups. The second lens group functions as a so-called focus group, and moves in the optical axis direction during focusing from infinity to a finite distance object. A configuration in which the second lens group is a focus group allows focusing to be performed by moving only a portion of the lens groups (only one lens group) that constitute the optical system, making it possible to reduce the size of the entire lens barrel of the optical system.

1-3. Equations Expressing the Conditions of the Optical System The optical system according to this embodiment employs the above-described configuration and preferably satisfies at least one of the following equations.
1.5<f1/f<7.0 (1)
however,
f: focal length of the optical system when focused at infinity f1: focal length of the first lens group

Formula (1) specifies the focal length of the first lens group and the focal length of the optical system when focused at infinity. Satisfying formula (1) is preferable from the viewpoint of realizing a compact optical system and good correction of aberrations. If f1/f exceeds the upper limit of formula (1), the power of the first lens group becomes weak, which leads to an increase in the size of the entire optical system, which is not preferable. On the other hand, if f1/f is less than the lower limit of formula (1), the power of the first lens group becomes strong, which is advantageous for compactness, but is not preferable because the amount of coma aberration and the like generated within the first group becomes large and correction becomes difficult. From the above viewpoint, f1/f is more preferably greater than 1.80, and even more preferably greater than 1.95. Also, from the above viewpoint, f1/f is more preferably less than 6.50, and even more preferably less than 6.10.

It is preferable that the optical system according to this embodiment satisfies the following conditions.
1.5<f2/f<5.0 (2)
however,
f: focal length of the optical system when focused at infinity f2: focal length of the second lens group

Formula (2) specifies the focal length of the second lens group and the focal length of the optical system when focusing at infinity. Satisfying formula (2) is preferable from the viewpoint of realizing a compact optical system in the radial direction and good correction of aberration. If f2/f exceeds the upper limit of formula (2), the power of the second lens group becomes weak, the amount of movement of the focus group becomes large, and the actuator for moving the focus group becomes large, which is not preferable. On the other hand, if f2/f is less than the lower limit of formula (2), the power of the second lens group becomes strong, which is advantageous for compacting the focus group, but is not preferable because the aberration fluctuation becomes large during focusing and correction becomes difficult. From the above viewpoint, f2/f is more preferably greater than 1.80, and even more preferably greater than 1.95. Also, from the above viewpoint, f2/f is more preferably less than 4.00, and even more preferably less than 3.50.

It is preferable that the optical system according to this embodiment satisfies the following conditions.
0.54<f1/f2<3.74 (3)
however,
f1: focal length of the first lens group f2: focal length of the second lens group

Formula (3) specifies the focal length of the first lens group and the focal length of the second lens group. It is preferable to satisfy formula (3) from the viewpoint of realizing a compact optical system and good correction of aberrations. When f1/f2 is equal to or greater than the upper limit of formula (3), the power of the first lens group is weakened, leading to an increase in the size of the entire optical system. When f1/f2 is equal to or less than the lower limit of formula (3), the power of the first lens group is strong, which is advantageous for compactness, but the amount of coma aberration and the like generated in the first lens group is large, making correction difficult. From the viewpoint of good correction of aberrations such as coma aberration, f1/f2 is more preferably greater than 0.62, and even more preferably greater than 0.70. Also, from the viewpoint of compactness of the optical system, f1/f2 is more preferably less than 3.46, and even more preferably less than 3.17.

It is preferable that the optical system according to this embodiment satisfies the following conditions.
0.78<f3/f1<7.33...(4)
however,
f1: focal length of the first lens group f3: focal length of the third lens group

Formula (4) specifies the focal length of the third lens group and the focal length of the first lens group. It is preferable to satisfy formula (4) from the viewpoint of realizing a compact optical system in the radial direction and good correction of aberration. When f3/f1 is equal to or less than the lower limit of formula (4), the power of the third lens group becomes strong and the power of the first lens group becomes weak. Therefore, the height of incidence of off-axis light rays into the third lens group becomes high, and the diameter of the third lens group becomes large. When f3/f1 is equal to or greater than the upper limit of formula (4), the power of the third lens group becomes weak and the power of the first lens group becomes strong. Therefore, it is advantageous for reducing the diameter of the third lens group, but the amount of coma aberration and the like generated in the first lens group becomes large, making correction difficult. From the above viewpoint, f3/f1 is more preferably greater than 0.89, and even more preferably greater than 1.00. Also, from the above viewpoint, f3/f1 is more preferably less than 6.77, and even more preferably less than 6.20.

It is preferable that the optical system according to this embodiment satisfies the following conditions.
0.12<β2<0.58...(5)
however,
β2: Lateral magnification of the second lens group when focused at infinity

Formula (5) specifies the lateral magnification of the second lens group. It is preferable to satisfy formula (5) from the viewpoint of realizing a compact optical system and good correction of aberrations. If β2 is equal to or greater than the upper limit of formula (5), the composite focal length of the first lens group and the second lens group becomes long and the power becomes weak, leading to an increase in the size of the entire optical system. If β2 is equal to or less than the lower limit of formula (5), the composite power of the first lens group and the second lens group becomes strong, which is advantageous for compactness, but the correction of coma aberration occurring within one group and the aberration fluctuation during focusing become large, making correction difficult. From the above viewpoint, β2 is more preferably greater than 0.13, and even more preferably greater than 0.15. From the above viewpoint, β2 is more preferably less than 0.53, and even more preferably less than 0.49.

It is preferable that the optical system according to this embodiment satisfies the following conditions.
Nd3<1.7...(6)
however,
Nd3: refractive index of the third lens for the d line

Formula (6) specifies the refractive index at the d-line of the third lens. Satisfying formula (6) is preferable from the viewpoint of improving the performance of the optical system. If Nd3 is equal to or greater than the upper limit of formula (6), the power of the third lens becomes strong, making it difficult to design a lens shape that is advantageous for correcting aberrations such as field curvature, which is not preferable from the viewpoint of improving performance. From the above viewpoint, Nd3 is more preferably less than 1.65, and even more preferably less than 1.60. From the above viewpoint, it is not necessary to specify a lower limit value for Nd3, but from the viewpoint of fully expressing the effects of the above viewpoint, it is sufficient if it is greater than 1.30, for example.

It is preferable that the optical system according to this embodiment satisfies the following conditions.
60<νd2max...(7)
however,
νd2max: maximum value of the Abbe number for the d-line of the lens in the second lens group

Formula (7) specifies the Abbe number for the d-line of the lenses in the second lens group. νd2max is the highest value of the Abbe number for the d-line of each lens constituting the second lens group. Satisfying formula (7) is preferable from the viewpoint of good correction of aberrations. If νd2max is equal to or less than the lower limit of formula (7), it becomes difficult to use a low-dispersion material in the second lens group, and therefore correction of axial chromatic aberration and lateral chromatic aberration becomes difficult. From the above viewpoint, νd2max is more preferably greater than 70, and even more preferably greater than 80. From the above viewpoint, it is not necessary to specify an upper limit value for νd2max, but from the viewpoint of fully expressing the effect of the above viewpoint, it is sufficient if it is less than 120.

It is preferable that the optical system according to this embodiment satisfies the following conditions.
νd123min<45...(8)
however,
νd123min: minimum value of the Abbe number for the d line in the first lens, the second lens, and the third lens

Formula (8) specifies the lowest Abbe number at the d-line among the first lens, the second lens, and the third lens. Satisfying formula (8) is preferable from the viewpoint of good correction of aberrations. If νd123min is equal to or greater than the upper limit of formula (8), it becomes difficult to correct lateral chromatic aberration and the like. From the above viewpoint, νd123min is more preferably less than 40, and even more preferably less than 36. From the above viewpoint, it is not necessary to specify a lower limit value for νd123min, but from the viewpoint of fully expressing the effects of the above viewpoint, it is preferable that it is greater than 10, for example.

It is preferable that the optical system according to this embodiment satisfies the following conditions.
60<νd321max...(9)
however,
νd321max: the maximum value of the Abbe number for the d-line in the (m-2)th lens, the (m-1)th lens, and the mth lens

Formula (9) specifies the highest Abbe number at the d-line of the three lenses in the third lens group, in order from the image side. νd321max is the highest Abbe number at the d-line of each of the three lenses in the third lens group, in order from the image side. Note that m is the total number of lenses in the optical system, and is preferably an integer of 7 or more. Satisfying formula (9) is preferable from the viewpoint of good correction of aberrations. If νd321max is equal to or less than the lower limit of formula (9), it becomes difficult to correct chromatic aberration of magnification and the like. From the above viewpoint, νd321max is more preferably greater than 65, and even more preferably greater than 70. From the above viewpoint, it is not necessary to specify an upper limit value for νd321max, but from the viewpoint of fully expressing the effect of the above viewpoint, it is preferable that it is less than 120.

It is preferable that the optical system according to this embodiment satisfies the following conditions.
0.5<(1-β2 ² )×β3 ² <1.5 (10)
however,
β2: Lateral magnification of the second lens group when focused on infinity β3: Lateral magnification of the third lens group when focused on infinity

Formula (10) shows the ratio of the movement amount of the image plane to the movement amount of the second lens group in the optical axis direction. Satisfying formula (10) is preferable from the viewpoint of miniaturization of the optical system and good correction of aberration. When (1-β2 ² )×β3 ² is equal to or less than the lower limit of formula (10), the movement amount of the second lens group increases, and the total optical length becomes long. When (1-β2 ² )×β3 ² is equal to or more than the upper limit of formula (10), it is advantageous for miniaturization of the focus group (second lens group), but the aberration fluctuation during focusing becomes large and correction becomes difficult. From the viewpoint of shortening the total optical length, (1-β2 ² )×β3 ² is more preferably greater than 0.7, and even more preferably greater than 0.9. Also, from the viewpoint of suppressing the aberration fluctuation during focusing, (1-β2 ² )×β3 ² is more preferably less than 1.3, and even more preferably less than 1.1.

2. Imaging Device Next, an imaging device according to an embodiment of the present invention will be described. The imaging device includes an optical system according to the above embodiment, and an imaging element provided on the image plane side of the optical system, which converts an optical image formed by the optical system into an electrical signal. The optical system in this embodiment is, for example, a fixed focal length lens.

Here, the imaging element is not limited, and solid-state imaging elements such as CCD (Charge Coupled Device) sensors and CMOS (Complementary Metal Oxide Semiconductor) sensors, silver halide film, infrared cut filters (IRCF), etc. can also be used. The imaging device according to this embodiment is suitable for imaging devices using the above-mentioned solid-state imaging elements, such as FA cameras, digital cameras, and video cameras. The imaging device may be a fixed-lens imaging device in which the lens is fixed to the housing, or may be an interchangeable-lens imaging device such as a single-lens reflex camera or a mirrorless single-lens camera.

Fig. 11 is a diagram showing a schematic example of the configuration of an imaging device according to this embodiment. As shown in Fig. 11, a mirrorless single-lens camera 1 has a body 2 and a lens barrel 3 that is detachable from the body 2. The mirrorless single-lens camera 1 is one form of an imaging device.

The lens barrel 3 has an optical system 30. The optical system 30 includes a first lens group 31, a second lens group 32, and a third lens group 33. The first lens group 31, the second lens group 32, and the third lens group 33 are all configured to have positive refractive power. The first lens group 31 includes at least a first lens, a second lens, and a third lens, in that order from the object side. The optical system 30 is configured to satisfy, for example, the above-mentioned expressions (1) and (2). An aperture 34 is disposed between the first lens group 31 and the second lens group 32.

The main body 2 has a cover glass 21 and a CCD sensor 22 as an imaging element. The CCD sensor 22 is disposed in the main body 2 at a position where the optical axis OA of the optical system 30 in the lens barrel 3 attached to the main body 2 is the central axis. Instead of the cover glass 21, the main body 2 may have an optical element that does not have substantial refractive power, such as an infrared cut filter.

The optical system in the embodiment of the present invention is configured as a small, high-performance optical system with a short overall length and large aperture by optimizing the power arrangement of the optical system and the movable group during focusing. And since the imaging device in the embodiment of the present invention is equipped with such an optical system, it is suitable for imaging devices that are short in length in the optical axis direction and require high-performance imaging, such as digital input/output devices such as in-vehicle cameras and drone-mounted cameras.

The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in the different embodiments are also included in the technical scope of the present invention.

An embodiment of the present invention will be described below. In the following tables, all lengths are in "mm" and all angles of view are in "°". "E-a" indicates "×10 ^-a ". In the first embodiment, the figures and tables are described, but the figures and tables in the first embodiment are similar to those in the other embodiments.

The optical systems of Examples 1 to 5 shown below are composed of, in order from the object side, a first lens group G1 having positive refractive power, an aperture stop S, a second lens group G2 having positive refractive power, and a third lens group G3 having positive refractive power. When focusing from infinity to an object at a finite distance, the first lens group G1 and the third lens group G3 remain fixed relative to the image plane IMG and do not move, while the second lens group G2 moves toward the object side along the optical axis.

[Example 1]
1 is a diagram showing a schematic diagram of the optical configuration of the optical system of Example 1 when focusing at infinity. In FIG. 1, "CG" is a cover glass, and "IMG" is an image plane (image formation plane). The arrow in the figure shows the movement of the second lens group G2 during focusing. The arrow indicates that the second lens group G2 moves approximately linearly within the range of the optical axis direction indicated by the arrow for focusing.

The first lens group is composed of, in order from the object side, a negative meniscus lens with a convex surface facing the object side, a negative meniscus lens with a convex surface facing the object side, a biconcave lens, a biconvex lens, a cemented lens consisting of a biconcave lens and a biconvex lens cemented together, and a positive meniscus lens with a convex surface facing the object side.

The second lens group is composed of, from the object side, a negative meniscus lens with a concave surface facing the object side, and a biconvex lens.

The third lens group is composed of, from the object side, a biconcave lens, a biconvex lens, and a biconvex lens.

Next, the optical characteristics of the optical system will be described. Table 1 shows the surface data of the optical system in Example 1.

In the examples, "Surface No." indicates the order of the lens surfaces when counting the lens surfaces of the optical system from the object side, "R" indicates the radius of curvature of the lens surface, "D" indicates the distance on the optical axis of the lens surfaces, "Nd" indicates the refractive index of the lens for the d-line (wavelength λ=587.56 nm), and "ABV" indicates the Abbe number of the lens for the d-line. "D(n)" (n is an integer) means that the distance on the optical axis of the lens surfaces is a variable distance that changes when focusing. In addition, "STOP" attached to the surface number indicates that it is an aperture, and "ASPH" indicates that the lens surface is aspheric. In addition, "0.0000" in the radius of curvature column indicates a flat surface.

[Table 1]
Surface No. RD Nd ABV
1ASPH 26.0430 1.4000 1.59201 67.02
2ASPH 9.8952 5.3267
3 22.5704 1.2000 1.48749 70.44
4 12.7286 9.0478
5ASPH -18.5000 1.1008 1.59270 35.45
6 130.2490 0.1500
7 44.9859 4.0760 1.87070 40.73
8 -68.9830 0.2105
9 -68.0398 0.8000 1.84278 24.68
10 22.7771 5.3948 1.86762 40.85
11 -29.8917 0.1500
12 37.2419 1.8271 1.92276 20.90
13 135.2267 10.2554
14STOP 0.0000 0.0000
15 0.0000 D(15)
16ASPH -17.1538 1.1000 1.76802 49.24
17ASPH -20.0000 0.4136
18 40.2480 5.3810 1.43700 95.10
19 -15.7851 D(19)
20 -30.5014 0.8000 1.75520 27.53
21 30.9331 1.4287
22 43.7865 4.4582 1.49700 81.61
23 -49.6670 0.1500
24 56.5324 5.4496 1.71117 55.67
25 -40.3279 13.1000
26 0.0000 2.0000 1.51680 64.20
27 0.0000 1.0000

Table 2 shows the specifications of the optical system of Example 1. The specifications show the numerical values of the optical characteristics at each shooting distance. In the specifications, "F" represents the focal length of the optical system at each shooting distance, "Fno" represents the F-number, and "W" represents the half angle of view. "D(0)" means the shooting distance. The shooting distance refers to the distance from the object to the first surface.

[Table 2]
F 13.1301 13.1331 13.1412
Fno 1.8023 1.8197 1.8812
W 48.5322 48.4523 48.1981
D(0) ∞ 380.8913 113.4998
D(15) 7.8693 7.4458 6.5654
D(19) 2.4107 2.8341 3.7146

Table 3 shows the aspheric coefficients of each aspheric surface in the optical system of Example 1. In the table, "K, A4, A6, A8, A10, A12" are the coefficients when the aspheric shape of each aspheric surface is defined by the following formula. In the formula, "Z" is the amount of displacement from the reference surface in the optical axis direction, "r" is the paraxial radius of curvature, "h" is the height from the optical axis in a direction perpendicular to the optical axis, "K" is the conic coefficient, and "An" is the n-th order aspheric coefficient.

[Table 3]
Surface No. K A4 A6 A8 A10
1 0.00000E+00 -4.16892E-05 1.43140E-07 -3.97690E-10 4.09977E-13
2 -5.88114E-01 -1.90902E-05 -2.24085E-07 2.86434E-09 -1.18741E-11
5 -3.66353E-01 -9.82977E-06 3.44722E-09 -1.57233E-09 1.48100E-11
16 8.84990E-01 3.79704E-05 9.21787E-07 -6.13394E-09 4.78012E-12
17 5.50000E-01 7.13104E-05 9.53551E-07 -6.27805E-09 1.76430E-11
Surface No. A12
1 0.00000E+00
2 0.00000E+00
5 -8.80257E-14
16 0.00000E+00
17 0.00000E+00

Figure 2 shows the longitudinal aberration of the optical system of Example 1 when focused at infinity. From the left side of the drawing, Figure 2 shows the spherical aberration (mm), astigmatism (mm), and distortion (%).

In the graph showing spherical aberration, the vertical axis represents the ratio to the maximum aperture F-number, and the horizontal axis represents defocus. In the graph showing spherical aberration, the solid line represents longitudinal aberration at the d-line (wavelength λ=587.56 nm), the dashed line represents longitudinal aberration at the F-line (wavelength λ=486.13 nm), and the dotted line represents longitudinal aberration at the C-line (wavelength λ=656.28 nm).

In the diagram showing astigmatism, the vertical axis represents the half angle of view (°) and the horizontal axis represents the defocus. In the diagram showing astigmatism, the solid line represents the sagittal image plane (S) for the d-line (wavelength λ = 587.56 nm), and the four-dot chain line represents the meridional image plane (T) for the d-line.

In the diagram showing distortion, the vertical axis represents half angle of view (°) and the horizontal axis represents distortion (%).

[Example 2]
The optical configuration of the optical system of Example 2 when focused at infinity is shown diagrammatically in Fig. 3, and the longitudinal aberration of the optical system of Example 2 when focused at infinity is shown in Fig. 4. Furthermore, surface data of the optical system of Example 2 is shown in Table 4, a specification table of the optical system of Example 2 is shown in Table 5, and the aspherical coefficients of each aspherical surface in the optical system of Example 2 are shown in Table 6.

[Table 4]
Surface No. RD Nd ABV
1ASPH 39.9427 1.4000 1.49700 81.61
2ASPH 9.4265 3.5775
3 15.9638 1.2000 1.72916 54.67
4 12.1785 9.2777
5ASPH -19.4383 0.9000 1.59270 35.45
6 71.4435 0.1500
7 40.9154 2.3521 1.87070 40.73
8 140.7261 0.1500
9 137.8193 0.8000 1.83848 24.02
10 22.5023 5.4755 1.87071 40.73
11 -27.9632 0.1500
12 38.8117 2.0050 1.92177 22.80
13 84.5581 10.0187
14STOP 0.0000 0.0000
15 0.0000 D(15)
16ASPH -19.6307 1.1000 1.76802 49.24
17ASPH -20.0000 0.1612
18 48.9442 7.5498 1.43700 95.10
19 -15.5927 D(19)
20 -42.4005 0.8000 1.75520 27.53
21 29.8838 1.5408
22 41.3057 4.3006 1.49700 81.61
23 -87.0548 0.1500
24 51.5872 5.9567 1.68806 57.08
25 -41.5968 13.2537
26 0.0000 2.0000 1.51680 64.20
27 0.0000 1.0000

[Table 5]
F 13.1309 13.1614 13.2276
Fno 1.8017 1.8128 1.8390
W 48.5308 48.4333 48.1354
D(0)∞ 382.1085 113.4998
D(15) 8.8183 8.3915 7.4867
D(19) 2.4124 2.8390 3.7440

[Table 6]
Surface No. K A4 A6 A8 A10
1 0.00000E+00 -2.63074E-05 9.71165E-08 -2.59247E-10 2.65454E-13
2 -5.78918E-01 -1.02442E-05 -3.81024E-07 3.85330E-09 -1.82641E-11
5 -3.66780E-01 -1.00568E-05 -3.73377E-09 -1.08659E-09 9.56013E-12
16 7.60554E-01 -4.68705E-06 8.38846E-07 -2.69831E-09 -2.07884E-11
17 5.50000E-01 4.34719E-05 9.06822E-07 -1.65054E-09 -1.19366E-11
Surface No. A12
1 0.00000E+00
2 0.00000E+00
5 -5.32552E-14
16 0.00000E+00
17 0.00000E+00

[Example 3]
The optical configuration of the optical system of Example 3 when focused at infinity is shown typically in Fig. 5, and the longitudinal aberration of the optical system of Example 3 when focused at infinity is shown in Fig. 6. Furthermore, surface data of the optical system of Example 3 is shown in Table 7, a specification table of the optical system of Example 3 is shown in Table 8, and the aspherical coefficients of each aspherical surface in the optical system of Example 3 are shown in Table 9.

[Table 7]
Surface No. RD Nd ABV
1ASPH 22.9749 1.4000 1.69350 53.20
2ASPH 9.9172 6.5857
3 31.0739 1.2000 1.48749 70.44
4 16.6992 10.0647
5ASPH -19.2217 0.9943 1.59270 35.45
6 226.0923 0.1500
7 47.3976 4.2405 1.87070 40.73
8 -34.8080 2.6428
9 -28.0991 0.8000 1.83718 25.66
10 25.1482 4.7066 1.86014 41.17
11 -28.3465 0.1500
12 33.8447 2.2028 1.92286 20.88
13 217.1861 6.6952
14STOP 0.0000 0.0000
15 0.0000 D(15)
16ASPH -19.2437 1.1000 1.76802 49.24
17ASPH -25.7394 0.1500
18 49.9875 5.2352 1.43700 95.10
19 -15.1080 D(19)
20 -23.3483 0.8000 1.75655 27.59
21 38.0483 0.9943
22 45.5796 5.8828 1.49700 81.61
23 -22.4177 0.1500
24 44.6153 3.8619 1.57683 67.21
25 -149.4437 13.1000
26 0.0000 2.0000 1.51680 64.20
27 0.0000 1.0000

[Table 8]
F 13.1290 13.0909 13.0150
Fno 1.8022 1.8083 1.8469
W 48.5355 48.5173 48.4082
D(0)∞ 380.2174 113.4996
D(15) 7.9822 7.5614 6.6977
D(19) 2.4112 2.8319 3.6958

[Table 9]
Surface No. K A4 A6 A8 A10
1 0.00000E+00 -4.79612E-05 1.67934E-07 -5.27689E-10 5.80644E-13
2 -7.16272E-01 -1.77836E-06 -1.36013E-07 3.43195E-09 -1.36534E-11
5 -3.05266E-01 -1.13786E-05 1.07416E-08 -2.51781E-09 2.41116E-11
16 1.00000E+00 2.78886E-05 4.56250E-07 -7.05197E-09 1.83092E-11
17 5.50000E-01 6.51795E-05 5.26657E-07 -6.57651E-09 2.56628E-11
Surface No. A12
1 0.00000E+00
2 0.00000E+00
5 -1.40214E-13
16 0.00000E+00
17 0.00000E+00

[Example 4]
The optical configuration of the optical system of Example 4 when focused at infinity is shown typically in Fig. 7, and the longitudinal aberration of the optical system of Example 4 when focused at infinity is shown in Fig. 8. Furthermore, surface data of the optical system of Example 4 is shown in Table 10, a specifications table of the optical system of Example 4 is shown in Table 11, and the aspherical coefficients of each aspherical surface in the optical system of Example 4 are shown in Table 12.

[Table 10]
Surface No. RD Nd ABV
1ASPH 24.4437 1.4000 1.59201 67.02
2ASPH 9.2285 6.3698
3 21.9555 1.2000 1.48749 70.44
4 13.7405 9.4893
5ASPH -17.7551 0.9264 1.59270 35.45
6 137.5973 0.1500
7 45.1277 1.8729 1.87070 40.73
8 74.9548 0.1500
9 69.0416 0.8000 1.85817 25.35
10 18.6049 5.2498 1.84834 41.68
11 -33.8920 3.5478
12 49.5046 2.3872 1.90366 31.31
13 -111.2074 7.2102
14STOP 0.0000 0.0000
15 0.0000 D(15)
16ASPH -22.4464 1.1000 1.76802 49.24
17ASPH -34.8800 0.2040
18 67.9726 3.0543 1.49700 81.61
19 -32.5687 0.1500
20 -145.9427 3.2076 1.43700 95.10
21 -20.0615 D(21)
22 -30.1711 0.8000 1.76156 27.83
23 32.8685 1.0836
24 39.7302 5.0153 1.49700 81.61
25 -35.6853 0.1500
26 45.5078 4.7492 1.57672 67.23
27 -61.0327 13.1000
28 0.0000 2.0000 1.51680 64.20
29 0.0000 1.0000

[Table 11]
F 13.1293 13.1031 13.0508
Fno 1.8022 1.8097 1.8640
W 48.5340 48.4860 48.3097
D(0)∞ 380.6584 113.4996
D(15) 7.7212 7.2994 6.4280
D(21) 2.4115 2.8331 3.7048

[Table 12]
Surface No. K A4 A6 A8 A10
1 0.00000E+00 -4.77052E-05 1.58917E-07 -4.78476E-10 5.55169E-13
2 -7.68123E-01 9.36725E-06 -2.25269E-07 4.24080E-09 -1.73590E-11
5 -2.84422E-01 -1.20803E-05 1.02844E-08 -2.71235E-09 2.54790E-11
16 1.00000E+00 1.97265E-05 2.21741E-07 -6.15642E-09 3.45123E-11
17 5.50000E-01 4.72518E-05 2.47566E-07 -5.50574E-09 3.20273E-11
Surface No. A12
1 0.00000E+00
2 0.00000E+00
5 -1.63714E-13
16 0.00000E+00
17 0.00000E+00

[Example 5]
The optical configuration of the optical system of Example 5 when focused at infinity is shown typically in Fig. 9, and the longitudinal aberration of the optical system of Example 5 when focused at infinity is shown in Fig. 10. Furthermore, surface data of the optical system of Example 5 is shown in Table 13, a specification table of the optical system of Example 5 is shown in Table 14, and the aspherical coefficients of each aspherical surface in the optical system of Example 5 are shown in Table 15.

[Table 13]
Surface No. RD Nd ABV
1ASPH 24.3621 1.4000 1.61881 63.85
2ASPH 9.8111 4.9374
3 20.7881 1.2000 1.58956 62.51
4 12.7309 9.1316
5ASPH -18.2738 1.1000 1.59270 35.45
6 107.9650 0.1500
7 47.6804 3.5160 1.87070 40.73
8 -77.1129 0.1500
9 -87.2396 0.8000 1.82874 24.39
10 22.6800 5.6150 1.87067 40.73
11 -29.7317 0.1500
12 38.4598 1.8210 1.92285 20.90
13 141.0519 10.7142
14STOP 0.0000 0.0000
15 0.0000 D(15)
16ASPH -17.4108 1.1000 1.76802 49.24
17ASPH -20.0000 0.3438
18 39.7191 5.3491 1.43700 95.10
19 -16.1216 D(19)
20 -33.0558 0.8000 1.75520 27.53
21 30.0340 1.4954
22 43.5601 4.3775 1.49700 81.61
23 -52.5415 0.1500
24 48.3176 5.7833 1.65656 59.31
25 -40.2833 13.1000
26 0.0000 2.0000 1.51680 64.20
27 0.0000 1.0000

[Table 14]
F 13.1302 13.1368 13.1524
Fno 1.8023 1.8204 1.8826
W 48.5321 48.4357 48.1458
D(0)∞ 381.1838 113.4998
D(15) 7.9047 7.4808 6.5959
D(19) 2.4111 2.8349 3.7199

[Table 15]
Surface No. K A4 A6 A8 A10
1 0.00000E+00 -4.38587E-05 1.34673E-07 -3.76469E-10 3.65763E-13
2 -5.57678E-01 -2.37021E-05 -2.57490E-07 2.83090E-09 -1.33215E-11
5 -3.97521E-01 -9.00257E-06 -3.49117E-09 -1.34181E-09 1.21248E-11
16 9.46745E-01 2.20281E-05 8.30470E-07 -2.19335E-09 -1.71584E-11
17 5.50000E-01 5.49863E-05 8.58563E-07 -2.92236E-09 -1.47224E-12
Surface No. A12
1 0.00000E+00
2 0.00000E+00
5 -6.84220E-14
16 0.00000E+00
17 0.00000E+00

The values calculated using the above formulas in Examples 1 to 5 and the numerical values used in the formulas are shown in Tables 16 and 17.

[Table 16]
Example 1 Example 2 Example 3 Example 4 Example 5
f 13.13 13.13 13.13 13.13 13.13
f1 40.39 78.78 26.26 31.72 43.49
f2 29.60 27.26 34.06 32.83 29.51
f3 87.06 86.34 144.76 134.34 87.59
β2 0.31 0.16 0.45 0.38 0.29
β3 1.05 1.01 1.12 1.08 1.04

[Table 17]
Example 1 Example 2 Example 3 Example 4 Example 5
(1) f1/f 3.08 6.00 2.00 2.42 3.31
(2) f2/f 2.25 2.08 2.59 2.50 2.25
(3) f1/f2 1.36 2.89 0.77 0.97 1.47
(4) f3/f1 2.16 1.10 5.51 4.24 2.01
(5) β2 0.31 0.16 0.45 0.38 0.29
(6) Nd3 1.59 1.59 1.59 1.59 1.59
(7) νd2max 95.1 95.1 95.1 95.1 95.1
(8) νd123min 35.4 35.4 35.4 35.4 35.4
(9) νd321max 81.6 81.6 81.6 81.6 81.6
(10) (1-β2 ² )×β3 ² 1.00 1.00 1.00 1.00 1.00

1. Mirrorless single-lens camera (imaging device)
2 Main body 3 Lens barrel 21 CG cover glass 22 CCD sensor (imaging element)
30 Optical system 31, G1 First lens group 32, G2 Second lens group 33, G3 Third lens group 34, S Aperture IMG Image surface OA Optical axis

Claims (14)

An optical system comprising, in order from an object side, a first lens group having positive refractive power, a second lens group having positive refractive power, and a third lens group having positive refractive power, the second lens group being movable along an optical axis so as to change a distance between adjacent lens groups during focusing ,
the first lens group includes, in order from an object side, at least a first lens, a second lens, and a third lens, the first lens and the second lens having negative refractive power;
the third lens group includes at least an (m-2)-th lens, an (m-1)-th lens, and an m-th lens, where m is a total number of lenses in the optical system;
An optical system that satisfies the following equation:
1.5<f1/f<7.0 (1)
1.5<f2/f<5.0 (2)
60<νd321max...(9)
however,
f: focal length of the optical system when focused at infinity, f1: focal length of the first lens group, f2: focal length of the second lens group
νd321max: the maximum value of the Abbe number for the d line in the (m-2) lens, the (m-1) lens, and the m lens 2. The optical system of claim 1, wherein the following formula is satisfied:
0.54<f1/f2<3.74 (3) 3. The optical system according to claim 1, which satisfies the following formula:
0.78<f3/f1<7.33...(4)
however,
f3: the focal length of the third lens group The optical system according to any one of claims 1 to 3, which satisfies the following formula:
0.12<β2<0.58...(5)
however,
β2: lateral magnification of the second lens group when focused on infinity The optical system according to any one of claims 1 to 4, which satisfies the following formula:
Nd3<1.7...(6)
however,
Nd3: refractive index of the third lens with respect to the d line The optical system according to any one of claims 1 to 5, which satisfies the following formula:
60<νd2max...(7)
however,
νd2max: the maximum value of the Abbe number for the d-line of the lens in the second lens group The optical system according to any one of claims 1 to 6, which satisfies the following formula:
νd123min<45...(8)
however,
νd123min: the minimum value of the Abbe number for the d line of the first lens, the second lens, and the third lens The optical system according to any one of claims 1 to 7 , which satisfies the following formula:
0.5<(1-β2 ² )×β3 ² <1.5 (10)
however,
β3: lateral magnification of the third lens group when focused on infinity The optical system according to claim 1 , wherein the first lens and the second lens are both negative meniscus lenses having a convex surface facing the object side. The optical system according to any one of claims 1 to 9 , wherein the second lens group is composed of three or less lenses. The optical system according to any one of claims 1 to 10 , wherein the first lens group has at least one cemented lens. The optical system according to claim 1 , wherein the lens in the second lens group closest to the object side has a concave surface facing the object side. 13. The optical system according to claim 1 , wherein the third lens group is composed of three or less lenses, includes at least one negative lens, and does not include an aspheric lens. An optical system according to any one of claims 1 to 13 ;
an image sensor provided on an image plane side of the optical system for converting an optical image formed by the optical system into an electrical signal;
An imaging device comprising:

Images